<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>a page</title>
<style>
html, body {
	margin: 0;
}

input {
	margin: 20px;
	width: 200px;
}
</style>

</head>

<body>
	<input id="input" type="text" placeholder="http://b.cros.com/b.html">
	<script>
		// URL: http://b.cors.com/b.html
		document.querySelector('#input').addEventListener('input', function() {
			window.parent.document.querySelector('input').value = this.value;
		})
		document.domain = 'cors.com';
	</script>
</body>

</html>
